The identification of tumor-associated antigenic markers have been exploited for diagnosis, surveillance and treatment of cancer. The development of monoclonal antibody technology has facilitated the search for phenotypic heterogeneity of tumors and normal tissues and the recognition of tumor-associated antigens. Monoclonal antibodies specific for the tumor-associated antigens can be used as targeting agents for the diagnosis and treatment of cancer. For example, antibodies can be used to detect tumors by means of immunoscintigraphic imaging and to treat tumors by immunotherapy. The lack of sufficient tumor specificity is still a problem. More selective antibodies are necessary to expand the clinician's armamentarium of anti-cancer agents.